Thanks John.

On Thu, Nov 11, 2004 at 07:56:10PM +1100, skaller wrote:
> By coercing TermType to ElType, you have coerced 'int' to 't',
> where 't' is an abstract type, in other words the coercion is hiding
> the representation. There are two ways around this

ok, I got the problem... but neither of your solutions solve my more
general problem as I need ElType.t to be an abstract data type as I'm
using it in a functor...

now it says:
This expression has type int but is here used with type
  SetOfTerm.Set.elt = TermType.t

for the same reason as before, but I can't change the ElType.t
without breaking the functor

[....]
module MakeSet =
    functor (Q : ElType) -> functor (SetFunc : SetFuncType) -> struct

    module Set = SetFunc ( struct
        type t = Q.t
        let compare = compare
    end
    )

[....]    

below the extended version of the problem with the same error...

any advice on how to modify my modules/classes design to overcome this
problem ? what I'm trying to do is to have set, setofset, setofsetofset 
etc using the same code base and functors...

:)
p

--------------------------------

module type ElType =
    sig
        type t
        val copy : t -> t
        val to_string : t -> string
    end

module type OrderedType =
    sig
        type t
        val compare : t -> t -> int
    end
  
module type SetFuncType =
    functor (Ord : OrderedType) ->
      sig
        type elt = Ord.t
        type t
        val empty : t 
        val compare : t -> t -> int
        val add : elt -> t -> t
      end

module MakeSet =
    functor (Q : ElType) -> functor (SetFunc : SetFuncType) -> struct

    module Set = SetFunc ( struct
        type t = Q.t
        let compare = compare
    end
    )

    class set ?(el=[]) () =
        object(self)
            initializer self#add el
            val mutable s = Set.empty
            method add el =
                s <- List.fold_left ( fun s' e -> Set.add e s' ) s el
        end
end

module TermType : ElType =
    struct
        type t = int
        let copy t = t
        let to_string t = "this is a string"
    end
;;

    
module SetOfTerm = MakeSet (TermType) (Set.Make);;

(* ------------------ *)

module SetOfTermType : ElType =
    struct
        type t = SetOfTerm.set
        let copy t = t
        let to_string t = "this is an other string"
    end
;;

module SetOfSet = MakeSet (SetOfTermType) (Set.Make);;

let newset_naked ?(el=[]) () = new SetOfTerm.set ~el:el
let newset ?(el=[]) () = (`Set (new SetOfTerm.set ~el:el))
let newsetofset ?(el=[]) () = (`Set (newset ~el:el ()))

let a = newset_naked ~el:[1;2] ();;
let b = newsetofset ~el:[a] ();;

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